Chart ColumnSeries yField issue

REQUIRED INFORMATION

Ext version tested:

Ext 4.1.3

Browser versions tested against:

IE9

Chrome

DOCTYPE tested against:

<!DOCTYPE html>

Description:

If yField is set up using a string, not an array of strings, then there is the first letter only in the Tip renderer. (Obviously, there is yField[0]. It needs to check there - it is an array or a string.)